I have written the following code:

			

			JTextPanel panel = new JTextPanel();
			

			panel.setBoxLayout(new BoxLayout(panel,BoxLayout.Y_AXIS));
			

			// adding many JTextPane
			s
			with text
			

			JScrollPane scroll = new JScrollPane(panel);
			

			scroll.getVerticalScrollBar().setValue(
			some big value for scrolling to middle of panel
			);
			

		

Now preferred size ( getPreferredSize() method) for the first (the upper) component in panel isn't correct. It seems that preferred size for non-visible components in ScrollPane is not evaluated. If I scroll up than scrolling is not smooth. While I'm scrolling up and upper component hasn't yet appeared, scrolling is smooth. When upper component is appearing I don't see underbody of component I see the component entirely. It seems that preferred size of the component is calculated only when the component should be appeared on the JScrollPane.

Can anybody explain this behaviour ?

How can I force calculating preferred size of all components of panel ?